ZTE NF Set solution helps the operator build a highly reliable 5GC network

Problems Faced by 5G Network

With the advent of the 5G, the 5G network have increased the transmission speed by more than 10 times compared with the 4G network, bringing about marvellous service experience for users, and AR/VR, cloud games etc high-traffic and low-latency requirements. In addition, 5G has greatly promoted specific industries such as V2X, unmanned routine check and intelligent manufacturing. 

Unlike the traditional customer-oriented consuming Internet, which focuses on voice call, instant communication and Internet services, the industrial applications focusing on Industrial Internet puts forward higher requirements on the robustness of 5G network: Industrial control network disconnection may lead to production line stagnation, V2X network disconnection may lead to traffic accidents, and network disconnection of telemedicine may put the patient's life in danger. Therefore, when the 5G network joins the ToB industry, it faces more strict reliability requirements. 

The traditional redundancy disaster recovery technology of the current network cannot meet the requirements of 5G industry services. For traditional Pool disaster recovery, when the DC fails or single NE failure occurs, all the online user sessions need to be re-established, and the user service interruption continue for a long time, maybe several minutes or even half an hour. In addition, signaling storms caused by the concurrent access of a large number of users may cause great risks to the network. Therefore, a more efficient and robust redundancy disaster recovery mechanism is urgently needed in the 5G network, which helps to meet the ultra-high reliability requirements of 99.9999% or 99.99999%. 

NF Set solution

To improve the reliability of the 5GC network, ZTE Common Core provides the 5GC NF (Network Function) Set solution (as shown in Figure 1). That is, the control plane NFs of the same type, the same service and the same slice can form a set cluster. The different NF instances in the same set can share the context data of the online services with each other, thus achieving the mutual redundancy changeover among the NF instances in the set, without interrupting the online services, and without affecting the new services. For example: AMF Set, SMF Set, etc..

Figure 1 NF Set Solution

Compared with the traditional NF Pool solution, the NF Set solution has the following features:

• The NF instances in NF Set share the online service context to implement service changeover without service interruption during the disaster recovery period. 
• The NF instances in NF Set support sharing the unified data storage service, thus enhancing network reliability and simplifying network deployment and O&M. 
• The NFs can be smoothly upgraded to support NF Set function, and the NF instances in a Set can run in different versions. 
• The NF Set not only reduces the number of redundant NF instances, but also improves network reliability and helps reduce network deployment costs. 

Online disaster recovery services are not affected

ZTE 5GC NFs are designed with a stateless architecture. The service context data is separated from the service logic processing. That is, the NF itself only provides the service logic processing function, and does not store the context of online services, and does not need to pay attention to the data redundancy backup mechanism. Instead, the independent data storage service implements the service context data redundancy disaster recovery mechanism. 

When an NF instance in the set fails, other NF instances can immediately take over the service processing of the failed NF and obtain the service context from the data storage service. When other NF instances take over the failed NF, there is no need to migrate data and online services are not interrupted, and users do not need to re-establish the sessions, which effectively avoids signaling storms caused by the re-access of a large number of users after the failed NF under the traditional Pool mechanism. 

Highly reliable and unified data storage

ZTE 5GC NF Set solution provides the storage service of context data through the unified UDSF (Unstructured Data Storage Function) (as shown in Figure 2). 

Figure 2 Distributed Data Storage UDSF

ZTE UDSF adopts distributed technical storage architecture to store and manage one or more NF Set session contexts in a unified database. Multiple DB instances are used to isolate different NF Sets data securely. UDSF supports 1+M copies redundancy and cross-resource pool and cross-DC geographic deployment mechanism to provide ultra-reliable redundancy and disaster recovery for data. 

ZTE UDSF also supports multiple flexible deployment modes. According to the network and service requirements of the operator, select a proper deployment mode:

• UDSF is built in each NF: It is unnecessary to maintain the independent UDSF. 
• Each NF Set exclusively occupies one UDSF: It is usually applicable to the different network slices. The use of independent UDSF can enhance the security isolation of the slices. 
• Multiple NF Sets share one UDSF: It helps to save construction and maintenance costs. 

Smooth upgrade and transformation of the existing network

The networking architecture of NF Set is similar to that of the traditional Pool solution. When 5GC NF is evolved from Pool solution into Set solution, the networking architecture does not need to be changed, it only needs to upgrade the adjacent NFs to support the selection of NF instances within an NF Set. In addition, if an NF instance in a Set fails, the adjacent NF needs to maintain the status of an online users and reselect another NF instance in the set to provide services. 

ZTE 5GC NF Set introduces the Cloud Native architecture. Similar to the grayscale release of microservices, the NF instances in a Set can run stably on different versions. The NF instances can be upgraded independently on demands, reducing the risks of upgrading all NF instances in a Set at a time. In addition, when an NF instance is upgrading, its online services can be taken over by other NFs without affecting the online services, and ensures the highly reliable service requirements without services interruption in specific industries. 

Hot redundancy with low-cost

In a NF Set, each NF instance adopts the N+M redundancy mechanism, which breaks the limitation of the traditional hot redundancy solution of 1+1 redundancy mechanism, reduces the number of redundant NF instances and provides higher reliability. 

In addition, the NF Set supports the shared UDSF, which avoids the defects that each NF instance needs to exclusively occupy a complete service component for the built-in data storage service. This reduces the number of public components and further reduces unnecessary waste of repeated resources. 
The disaster recovery detection and service changeover mechanism of NF Set are automatically carried out according to the definition of 3GPP standards. The coordination with the adjacent NFs does not need manual intervention. The operation and maintenance is simple and its cost are reduced. 

Conclusion

ZTE 5GC NF Set solution provides the operators with a 5GC NF hot redundancy solution with lower costs and more reliability . While constructing a more perfect and robust 5GC network, it also helps to lay a solid technical foundation for 5G to successfully enter the industrial Internet fields where need a network transmission without service interruption.